1 Field of the Invention
This invention relates to an FM stereo signal demodulator for separating a composite FM stereo signal into left and right signals. In particular, this invention relates to an FM stereo signal demodulator wherein the amplitude of the 38 kHz switching signal necessary to separate the composite signal into left and right signals is varied, thereby making it possible to alter the degree of left and right signal separation and to achieve a good signal to noise ratio (S/N) for received signals having a wide range of electric field strengths.
2 Description of the Prior Art
When an FM stereo signal is received and the electric field strength is somewhat higher than the limiting sensitivity of the receiver, stereo reception is adversely affected in signal to noise ratio by nearly 20 dB in comparison with monaurel reception. This difference in signal to noise ratio varies depending on the degree of separation of the composite stereo signal, the signal to noise ratio being worse the greater the degree of the separation.
Thus to obtain a good signal to noise ratio over a wide range of electric field strengths, the left and right signal separation should be controlled such that the separation is large when the electric field is strong, and such that the separation becomes smaller as the electric field strength becomes weaker.